LARES Lexicon Acoustic Reverberance Enhancement System exicon How LARES can Help Meet the Objectives of Good Acoustical Design". Sound Reinforcement Reinforcing Early Reflections In this application LARES principles yield an in­ The perceived loudness of a sound in a hall depends crease in gain-before-feedback of 6 -18 dB. The both on the loudness of the direct sound and on the amount of improvement depends on the number of amount of early reflected energy which adds to the microphones, loudspeaker channels, and number direct sound. The level of the first few strong of Lexicon's Advanced DSP processors. For ex­ reflections is determined primarily by the hall ge­ ample, the increase is 15 dB with two microphones, ometry. Careful placement of reflecting surfaces in four loudspeaker channels, and one Lexicon 480L the stage, ceiling and side walls can increase this Advanced DSP. With two processors and eight level somewhat by directing sound energy to the loudspeaker channels, the improvement is 18 dB. audience. However, the energy directed to the audience by walls or reflectors is generally ab­ With such a large increase in gain before feedback sorbed, and is not available to create additional level far fewer microphones need to be employed to or later reverberation. For this and many other reinforce any performance, and the reinforcement is reasons, the total amount of reflected energy de­ hard to distinguish from the natural response of the pends primarily on the amount of absorption in the hall. This type of reinforcement is ideal for boosting hall, which in most halls is proportional to the seating a weak vocalist or chorus in a show, improving stage area. The more people you put in a hall the softer the acoustics through added reflected energy, or add­ sound will be. ing lateral reflections to a hall. In reinforcement applications the LARES software is adjusted to This conflict between hall loudness and seating area provide maximum intelligibility and minimum rever­ is fundamental. It means that small halls will always beration. LARES software also incorporates time sound louder than larger ones, and when a small delays that can be adjusted to insure that the rein­ orchestra plays in a large hall, the sound will not forced sound matches the direct sound. have the the impact and richness that enough level can create. Acoustic Enhancement LARES can help enormously with this classic acous­ tic dilemma. Since the loudspeakers add energy Spaces that can benefit from LARES may vary in (from the power company) loudness can be in­ size, absorptivity and use. By distinguishing some creased without the penalty to later reverberation. of the desirable properties of rooms used for listen­ To significantly increase the actual acoustic level a ing to music and identifying typical problems en­ large amount of acoustic power will be required - at countered in acoustic spaces, we can see how least as much as the orchestra itself! If a conven­ LARES can be integrated to improve the acoustic tional sound reinforcement system were used to design. provide the power, normal microphone spacings of LARES Matches the Space to the Performance", Reverberance Desired for Various Types of Performance 111111 ••••••••••• Symphony (Romantic Works) 1111111;1111 I III Secu Iar Chor aI Works 11111111,1111~_.i 1111111 Contempor ar y Or chestral WorkS, Recital and Chamber Mus ic 1111111 111 '11111 Ope r a I 1111 11111 Semiclassical Concer ts and Choral Groups Us ing Sound System I 11111111 : : ~ 11111111) I I I Tour ing Br oadway Musical Comed ies, Operettas, Gilbert & Sullivan I .11111111 111,1111111 Dance Bands Etc. Us ing Sound System '11111111 III 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 ReverberationTime in Seconds Reverb Times Typical for Various Performance Spaces I I I I I I Small Churches Large Churches Cathedrals 1111111 i Concert Halls .I. 111)1111111 11111111111 Gen era l Pu rpose Au di tori ums 11111111111 11111111 I I Hi gh Sc hoo l Au ditor iums 1111111111 III 1111 Smal I Theatres 1111fIIlII~ 1111 Cinema I 11I11II._allll Lecture and Conference Rooms 1111 III El ementary Classr ooms I III 1111 I Rec ording and broadcast studies for spe ech only II rl.,-II .1 I I I I 1 I 1 I I I I I I I I I I 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 ReverberationTime in Seconds As shown in the charts above, spaces often do not provide reverberation that is well suited lor different types 01 performance. LARES can help spaces achieve reverberant characteristics appropriate for both specific and multipurpose use. one meter or less would be required to achieve designed which project reflected energy primarily to adequate level while maintaining low coloration. In the walls instead of directly down on the audience, this application, LARES adds both the reinforce­ and the walls of fan shaped halls can be staggered ment necessary to achieve adequate acoustical so sound reflects primarily back across the audito­ power and provides reverberant enhancement. With rium. LARES, a much greater microphone distance can be used eliminating the need for operator interven­ Such features may increase the lateral fraction, but tion or a carefully mixed close microphone array. may not increase the total lateral energy. The And unlike a conventional reinforcement system, features are probably a good idea, but even with the energy added from LARES will not be audibly them LARES can help considerably. In our experi­ artificial. ence and that of J . Bradley at the NRC in Canada, spaciousness depends primarily on the absolute Where the initial time delay gap in an existing hall is strength of the lateral energy, not necessarily in the too large the LARES software and an array of early lateral fraction. LARES systems are particu­ speakers (hidden in the ceiling or disguised as larly effective in raising the lateral energy, and can lighting or sculpture) can fill in the missing energy, be designed to increase the early lateral fraction if and do it without any artificial tone color. Such a this is desired. LARES array can also supply the missing lateral energy in fan shaped designs without any alteration We have found that a uniform ceiling array of high to the desirable sight lines such shapes provide. quality non-directional speakers combined with our multi-channel digital electronics can successfully In larger spaces, the control of reverberation time create a diffuse sound field with high lateral energy. and level that LARES provides makes it possible to In the Elgin Theater (Toronto, Ontario, Canada) 56 design a large hall with short audience seating speakers under the balcony combined with special distances and good sight lines while maintaining LARES software and hardware produce a sound world class reverberance. Such a hall could be field which seems to come from all around the optimized for both symphony and opera, with their listeners, even if they stand only 5 feet below one of very different acoustical requirements. The LARES the speakers. There are no echoes even on percus­ equipped hall would have the advantage of adjust­ sive material, and the sound field does not reduce able acoustics without the expense of motorized the intelligibility of speech. The lateral energy in­ drapes or mechanical doors opening to reverbera­ creases at least 4 dB when this array is activated, tion chambers. Since changes to the reverberation and the increase in spaciousness is impressive. are silent and fast, it is easy to optimize the hall for The ceiling seems to disappear, to be replaced by a a particular piece in real time. With the A. R. C. very convincing illusion of the hall above. (Automatic Reverberance Control) circuit provided in LARES, it is also possible to achieve a much Improved Control Over Late higher richness and spaciousness in opera produc­ tions without compromising dialog. Reverberation Level Enhanced Spaciousness Our experience with recorded music has lead us to believe that the ratio of direct sound to reverberant sound is quite critical. Too little reverberant level The vital acoustic property of spaciousness or spa­ and music sounds flat and lifeless. Too much makes tial impression depends on having adequate reflec­ the sound garbled and muddy. The same appears tions that come from the sides of the listener. With­ to be true of halls. In classical acoustics this ratio out electro-acoustics, the direction of reverberation depends primarily on the geometry of the hall and energy depends primarily on the shape of the hall. where you sit, but in the best halls the reverberant Halls of rectangular or inverse fan shape have a sound is never inaudible, and the music is never higher fraction of early lateral reflections than square obscured. or fan shaped halls. Once the importance of lateral energy was recognized by acousticians many clever ways increasing it were invented and incorporated into hall designs. For example, ceilings can be • The reverberant level also depends on the size of In a small hall the problem is reversed. Conven­ the hall. In a small hall there may not be adequate tional wisdom for designing such a space would try audience seating area to absorb the sound. The to make every surface that did not hold the audience reverberant level can be high, and the reverberation as reflective as possible in an effort to increase the time can be too short.